By Andrew Russeth The BTS leader has been championing canonical artists from his native South Korea — studying their work, buying it and sometimes talking to it. “I feel like they’re watching me,” he said.SEOUL — RM, the leader of the South Korean pop group BTS, first visited Grand Central Terminal in Manhattan to perform for Jimmy Fallon’s “Tonight Show.” It was early 2020, before the coronavirus lockdown, and in middle of the night, joined by a sizable dance crew, BTS’s seven members put ...